Analog-to-digital converters (ADCs) and, in particular, continuous-time sigma-delta modulators (CTSDMs) are gaining popularity due to power-efficient operation well-suited for high-speed, high-performance systems. In a CTSDM, typically an input analog signal that varies over time is converted into a digital stream that represents the input with high fidelity in the frequency band of interest. This digital stream then goes through digital post-processing (typically decimation) to provide the final digital code stream which represents the analog input signal in the digital domain with high fidelity.
However, in one approach, CTSDMs use a current digital-to-analog converter (DAC) in a feedback path that can suffer from input-dependent reference errors. Though techniques such as quad-switching have been used to address such errors, CTSDMs as well as other ADCs and DACs are also susceptible to external reference noise. For example, values of external components such as voltage references may drift with temperature and over time, which adversely impacts performance.